1. Field
This disclosure relates generally to non-volatile memories, and more specifically, to a non-volatile memory having a static verify-read output data path.
2. Related Art
Floating gate non-volatile memories such as erasable programmable read only memories (EPROMs), electrically erasable programmable read only memories (EEPROMs), block erasable (“flash”) EEPROMs, and one time programmable read only memories (OTPROMs) are popular for many electronic applications such as automotive control, consumer products such as tapeless answering machines, and the like. In floating gate memories, a programmed state of each memory cell is determined by the amount of charge stored on a floating gate. The stored charge determines the threshold voltage (VT) of the cell. The floating gate is isolated from an underlying channel by a region of tunnel oxide. Typically, the floating gate transistor is programmed and erased by processes known as Fowler-Nordheim tunneling and hot carrier injection. Care must be taken when programming or erasing a non-volatile memory cell to fully shift the VT while avoiding over programming or over erasing the cell. One way to protect against over erasing or over programming is to use multiple program or erase pulses with a verify-read operation after each pulse to determine if the cell is fully programmed or erased.
In some flash memories, a separate read path is used for verify operations. The separate verify path is used to allow a program or erase operation to occur at the same time as a normal read operation. The verify read output path is separate from the normal read path so that flash performance is not affected. One prior art flash memory uses a tristateable driver coupled to a verify global data line dedicated to verify-read operations.
The use of a tristateable driver requires the overhead of timed control signals to properly precharge and evaluate the verify global data line. Also, the tristateable driver is usually single-ended and does not easily allow the use of a symmetrical sense amplifier layout. A symmetrical sense amplifier that uses differential signals is desirable for more reliable high speed sensing. In addition, the tristateable driver typically requires a large surface area of an integrated circuit die to implement, thus increasing the size and cost of the integrated circuit.
Therefore, a need exists for a way to solve the above problems.